Table reference discrepancy

[Silva]

I'm new to AppSheet so this question may be simple for some of you. I have two tables (Clientes and Contratos), where each client has one or more contracts so the contracts table references clients table. The problem is that I have a discrepancy between my AppSheet data source and the app data preview when looking at the contracts table:

This is the source data:

And this is the app preview data:

So I'm trying to reference rut, but it is instead referencing the row Id column that AppSheet created automaticaly when the app was created (rut is already set as key inside the app).
How do I solve?

Thanks

[AleksiAlkio]

The Ref column is always referenced to parent's table key column because it needs to be unique. If you want to use Rut column, you need to select it as the key column.